This work combines spectroscopic and photometric data of the polluted white
dwarf WD0141-675 which has a now retracted astrometric super-Jupiter candidate
and investigates the most promising ways to ...confirm Gaia astrometric planetary
candidates and obtain follow-up data. Obtaining precise radial velocity
measurement for white dwarfs is challenging due to their intrinsic faint
magnitudes, lack of spectral absorption lines, and broad spectral features.
However, dedicated radial velocity campaigns are capable of confirming close in
giant exoplanets (a few M$_{\textrm{Jup}}$) around polluted white dwarfs, where
additional metal lines aid radial velocity measurements. Infrared emission from
these giant exoplanets is shown to be detectable with JWST MIRI and will
provide constraints on the formation of the planet. Using the initial Gaia
astrometric solution for WD0141-675 as a case study, if there were a planet
with a 33.65 d period or less with a nearly edge on orbit, 1) ground-based
radial velocity monitoring limits the mass to $<$ 15.4 M$_{\textrm{Jup}}$, and
2) space-based infrared photometry shows a lack of infrared excess and in a
cloud-free planetary cooling scenario, a sub-stellar companion would have to be
$<$ 16 M$_{\textrm{Jup}}$ and be older than 3.7 Gyr. These results demonstrate
how radial velocities and infrared photometry can probe the mass of the objects
producing some of the astrometric signals, and rule out parts of the brown
dwarf and planet mass parameter space. Therefore, combining astrometric data
with spectroscopic and photometric data is crucial to both confirm, and
characterise astrometric planet candidates around white dwarfs.
The photospheric metal pollution of white dwarfs is now well-established as the signature of the accretion of planetary debris. However, the origin of the trace hydrogen detected in many white dwarfs ...with helium atmospheres is still debated. Here, we report the analysis of GD424: a metal-polluted, helium-atmosphere white dwarf with a large amount of trace hydrogen. We determined the atmospheric parameters using a hybrid analysis that combines the sensitivity of spectroscopy to the atmospheric composition, \(\log(\mathrm{H/He})\), with that of photometry and astrometry to the effective temperature, \(T_{\mathrm{eff}}\), and surface gravity, \(\log g\). The resulting white dwarf mass, radius, and cooling age are \(M_{\mathrm{WD}}=0.77\pm0.01\,\mathrm{M}_{\odot}\), \(R_{\mathrm{WD}}=0.0109\pm0.0001\,\mathrm{R}_{\odot}\), and \(\tau_\mathrm{cool}=215\pm10\) Myr, respectively. We identified and measured the abundances of 11 photospheric metals and argue that the accretion event is most likely either in the increasing or steady state, and that the disrupted planetesimal resembles either CI chondrites or the bulk Earth in terms of its composition. We suggest that the observed \(1.33\times 10^{22}\) g of trace hydrogen in GD424 were at least partly acquired through accretion of water-rich planetary debris in an earlier accretion episode.
Stars with excess infrared radiation from circumstellar dust are invaluable for studies of exoplanetary systems, informing our understanding on processes of planet formation and destruction alike. ...All-sky photometric surveys have made the identification of dusty infrared excess candidates trivial, however, samples that rely on data from WISE are plagued with source confusion, leading to high false positive rates. Techniques to limit its contribution to WISE-selected samples have been developed, and their effectiveness is even more important as we near the end-of-life of Spitzer, the only facility capable of confirming the excess. Here, we present a Spitzer follow-up of a sample of 22 WISE-selected infrared excess candidates near the faint-end of the WISE detection limits. Eight of the 22 excesses are deemed the result of source confusion, with the remaining candidates all confirmed by the Spitzer data. We consider the efficacy of ground-based near-infrared imaging and astrometric filtering of samples to limit confusion among the sample. We find that both techniques are worthwhile for vetting candidates, but fail to identify all of the confused excesses, indicating that they cannot be used to confirm WISE-selected infrared excess candidates, but only to rule them out. This result confirms the expectation that WISE-selected infrared excess samples will always suffer from appreciable levels of contamination, and that care should be taken in their interpretation regardless of the filters applied.
WD 0145+234 is a white dwarf that is accreting metals from a circumstellar disc of planetary material. It has exhibited a substantial and sustained increase in 3-5 micron flux since 2018. Follow-up ...Spitzer photometry reveals that emission from the disc had begun to decrease by late 2019. Stochastic brightening events superimposed on the decline in brightness suggest the liberation of dust during collisional evolution of the circumstellar solids. A simple model is used to show that the observations are indeed consistent with ongoing collisions. Rare emission lines from circumstellar gas have been detected at this system, supporting the emerging picture of white dwarf debris discs as sites of collisional gas and dust production.
Gliese 86 is a nearby K dwarf hosting a giant planet on a $\approx$16-day
orbit and an outer white dwarf companion on a $\approx$century-long orbit. In
this study we combine radial velocity data ...(including new measurements spanning
more than a decade) with high angular resolution imaging and absolute
astrometry from Hipparcos and Gaia to measure the current orbits and masses of
both companions. We then simulate the evolution of the Gl 86 system to
constrain its primordial orbit when both stars were on the main sequence; the
closest approach between the two stars was then about $9\,$AU. Such a close
separation limited the size of the protoplanetary disk of Gl 86 A and
dynamically hindered the formation of the giant planet around it. Our
measurements of Gl 86 B and Gl 86 Ab's orbits reveal Gl 86 as a system in which
giant planet formation took place in a disk truncated at $\approx$2$\,$AU. Such
a disk would be just big enough to harbor the dust mass and total mass needed
to assemble Gl 86 Ab's core and envelope, assuming a high disk accretion rate
and a low viscosity. Inefficient accretion of the disk onto Gl 86 Ab, however,
would require a disk massive enough to approach the Toomre stability limit at
its outer truncation radius. The orbital architecture of the Gl 86 system shows
that giant planets can form even in severely truncated disks and provides an
important benchmark for planet formation theory.
This paper presents the results of an extensive search for substellar companions to white dwarfs in the solar neighborhood. The work consists of two major components. The first part is a survey ...conducted with the Keck I 10 meter telescope of 86 white dwarfs. This deep near field search was sensitive to companions orbiting between roughly 50–1100 AU of the primary star. The second part is a wide field survey conducted with the Bok 2.3 meter and Shane 3 meter telescopes of 261 white dwarfs. This latter search was sensitive to companions orbiting between roughly 100–5000 AU. The entire sample has a median distance of around 57 pc. The J band, centered at 1.25 μm, was chosen as the appropriate wavelength to conduct this search. This atmospheric window lies near the peak in luminosity of substellar objects, commonly called brown dwarfs. The mass limits of the searches are dependent on the age of the white dwarfs in the sample because brown dwarfs cool as they evolve. The exact ages of the target primaries cannot be known because of their uncertain main sequence progenitor lifetimes. However, for white dwarfs about 3 Gyrs old, a reasonably conservative median age estimate, companions more massive than 0.06 special characters omitted in the wide field search and more massive than 0.03 special characters omitted in the deeper near field search were detectable. In neither component of the survey were any brown dwarf candidates detected. This implies a brown dwarf companion fraction of less than 0.3% for white dwarfs. In stark contrast, the stellar companion fraction of white dwarfs as measured by this survey is 22%. Moreover, most of the known and suspected stellar companions to white dwarfs are low mass stars whose masses are only slightly greater than the masses of brown dwarfs. This result has strong implications for binary star formation. Twenty previously undiscovered stellar companions were detected, five of which are confirmed or likely white dwarfs themselves. The remaining fifteen detected companions are confirmed or likely low mass stars.
White dwarfs with metal-polluted atmospheres have been studied widely in the context of the accretion of rocky debris from evolved planetary systems. One open question is the geometry of accretion ...and how material arrives and mixes in the white dwarf surface layers. Using the 3D radiation-hydrodynamics code CO\(^5\)BOLD, we present the first transport coefficients in degenerate star atmospheres which describe the advection-diffusion of a passive scalar across the surface-plane. We couple newly derived horizontal diffusion coefficients with previously published vertical diffusion coefficients to provide theoretical constraints on surface spreading of metals in white dwarfs. Our grid of 3D simulations probes the vast majority of the parameter space of convective white dwarfs, with pure-hydrogen atmospheres in the effective temperature range 6000-18000 K and pure-helium atmospheres in the range 12000-34000 K. Our results suggest that warm hydrogen-rich atmospheres (DA; \(\gtrsim\)13000 K) and helium-rich atmospheres (DB, DBA; \(\gtrsim\)30000 K) are unable to efficiently spread the accreted metals across their surface, regardless of the time dependence of accretion. This result may be at odds with the current non-detection of surface abundance variations at white dwarfs with debris discs. For cooler hydrogen- and helium-rich atmospheres, we predict a largely homogeneous distribution of metals across the surface within a vertical diffusion timescale. This is typically less than 0.1 per cent of disc lifetime estimates, a quantity which is revisited in this paper using the overshoot results. These results have relevance for studies of the bulk composition of evolved planetary systems and models of accretion disc physics.
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